Miss Lizzie,
I think you are starting to over think this quilt and drive yourself crazy. Take a deep breath and decide how you are going to do this. You seem attracted to the random width stripes and that should not be too hard to do. One of the patterns you've shown was tied instead of quilted. That should be easy enough to do, too.
If you can cut a straight line and sew a straight seem, you can get this done. Unless your sister is a member of the quilt police, it will all work out fine in the end.
Take it easy and try to have some fun with this. :)